Development of the K -stiffness method for geosynthetic reinforced soil walls constructed with c -ϕ soils (original) (raw)
Related papers
Can Geotech J, 2007
In this paper the K-stiffness method is extended to the case of c-soils using data obtained from a total of nine new case studies -six from Japan and three from the USA. A common feature in this new data set is that the walls were all constructed with a vertical face using backfill soils with a range of fines content. The walls varied widely with respect to facing type. This new data set together with previously published data for vertical walls is now used to isolate the effect of soil cohesion on reinforcement loads within the framework of the original K-stiffness method. The new data set is used to calibrate a modified K-stiffness method equation that includes a cohesion influence factor. The modified K-stiffness method is demonstrated to quantitatively improve the estimate of the magnitude and distribution of reinforcement loads for internal stability design of vertical-faced geosynthetic reinforced soil walls with c-soil backfills when compared to the current American Association of State Highway and Transportation Officials simplified method.
Refinement of K-stiffness Method for geosynthetic-reinforced soil walls
Geosynthetics International, 2008
The K-stiffness Method is an empirically-developed working stress method used to compute reinforcement loads for the internal stability design of geosynthetic-reinforced soil walls under serviceability conditions. In this paper, additional data from Japanese case studies for five full-scale field and three full-scale laboratory geosynthetic-reinforced soil walls are added to the database that was used to calibrate the original K-stiffness Method. One more case study from an instrumented wall in the USA is also introduced. Measured loads are compared with predicted loads using the current AASHTO Simplified Method and a modified version of the K-stiffness Method that has been adjusted by back-fitting model parameters to the extended database. The AASHTO Simplified Method is shown to be excessively conservative (on average) with respect to accurate prediction of reinforcement loads and to correlate poorly with measured values. The modified K-stiffness Method is demonstrated by statistical analysis to give ratios (bias) of average measured to predicted reinforcement load values close to 1 and coefficient of variation (COV) values for the maximum reinforcement load in a wall that are less than 25%.
Evaluation of K-Stiffness Method for Vertical Geosynthetic Reinforced Granular Soil Walls in Japan
SOILS AND FOUNDATIONS, 2007
In this paper the K-stiŠness Method as originally proposed by is re-examined using a total of six new case studies-ˆve from Japan and one from the USA. A common feature of the walls in this new data set is that the walls were all constructed with a vertical face and a granular backˆll. However, the walls varied widely with respect to facing type. This new data set together with data for vertical walls previously published by Allen and Bathurst (2002a,b) and is now used to isolate the eŠect of the facing stiŠness factor on reinforcement loads and to adjust the original equation that was developed to calculate its value. The paper also shows that predicted reinforcement loads using the current AASHTO Simpliˆed Method in the USA and the current PWRC method in Japan give the same reinforcement load predictions, and both grossly over-estimate the values deduced from measured strains. The new data set is used to slightly reˆne the estimate of the facing stiŠness factor used in the original K-stiŠness Method. The original and modiˆed K-stiŠness Method are demonstrated to quantitatively improve the estimate of the magnitude and distribution of reinforcement loads for internal stability design of vertical-faced geosynthetic reinforced soils walls with granular backˆlls when compared to the current American and Japanese methods.
Application of the Simplified Stiffness Method to Design of Reinforced Soil Walls
Journal of Geotechnical and Geoenvironmental Engineering, 2018
A new design methodology for estimating reinforcement loads in reinforced soil walls, termed the K 0-Stiffness Method, has been developed. This new method has been demonstrated to more accurately estimate reinforcement loads and strains in reinforced soil walls than do current design methodologies. Step-by-step procedures are provided to lead the designer through the reinforced soil wall internal stability design process using this new methodology. These step-by-step design procedures have been developed with a limit states design approach consistent with current design codes (in North America this is termed Load and Resistance Factor Design, or LRFD). Specifically, consideration has been given to strength and serviceability limit states. Load and resistance factors, based on statistical data where feasible, have been developed for use with this method. The results of examples from actual wall case histories were summarized and analyzed to assess how well the new methodology performs relative to current design practice. From this analysis of the design examples, the following was observed: • For geosynthetic walls, the K 0-Stiffness Method has the potential to reduce required backfill reinforcement capacity relative to current design methodology by a factor of 1.2 to 3. • For steel reinforced soil walls, the reduction in reinforcement capacity relative to what is required by current design methodology is more modest, on the order of 1.0 to 2.1. Given these findings, use of the K 0-Stiffness Method can result in substantial cost savings, especially for geosynthetic walls, because of reduced reinforcement needs.
Canadian Geotechnical Journal, 2006
Current limit equilibrium-based design methods for the internal stability design of geosynthetic reinforced soil walls in North America are based on the American Association of State Highway and Transportation Officials (AASHTO) Simplified Method. A deficiency of this approach is that the influence of the facing type on reinforcement loads is not considered. This paper reports the results of two instrumented full-scale walls constructed in a large test facility at the Royal Military College of Canada. The walls were nominally identical except one wall was constructed with a stiff face and the other with a flexible wrapped face. The peak reinforcement loads in the flexible wall were about three and a half times greater than the stiff-face wall at the end of construction and about two times greater at the end of surcharging. The stiff-face wall analysis using the Simplified Method gave a maximum reinforcement load value that was one and a half times greater than the measured value at ...
Geosynthetics International, 2009
The paper describes measurements taken from a series of four full-scale modular block walls that were constructed with reinforcement layers having different stiffness. The walls were 3.6 m high and were reinforced with two different polypropylene geogrid reinforcement materials, a polyester geogrid and a welded wire mesh. Each wall was constructed with the same modular block facing and reinforcement spacing of 0.6 m. The influence of compaction effort on wall displacements and horizontal toe load measurements at the end of construction was detectable in this investigation. These values were adjusted to account for the influence of different compaction methods on end-of-construction wall response. However, during subsequent surcharging the effects of initial compaction effort were erased. Reinforcement loads are computed from strain readings and results of in-isolation constant-load (creep) tests. Computed maximum reinforcement loads are compared with values predicted using the current AASHTO Simplified Method and the K-stiffness Method. The predicted magnitude and distribution of reinforcement loads are shown to be more accurate using the K-stiffness Method for polymeric reinforcement materials. For the relatively stiff welded wire mesh product, the measured reinforcement loads fell between values predicted using both methods.
Prediction of reinforcement loads in reinforced soil walls
Proper estimation of soil reinforcement loads and strains is key to accurate design of the internal stability of geosynthetic and steel reinforced soil structures. Current design methodologies use limit equilibrium concepts to estimate reinforcement loads for internal stability design, with empirical modifications to match the prediction to observed reinforcement loads at working stresses. This approach has worked reasonably well for steel reinforced walls but appears to seriously overestimate loads for geosynthetic walls. A large database of full-scale geosynthetic walls (16 fully instrumented, full-scale geosynthetic walls and 14 walls with limited measurements) and 24 fully instrumented, full-scale steel reinforced wall sections was utilized to develop a new design methodology based on working stress principles, termed the K-Stiffness Method. This new methodology considers the stiffness of the various wall components and their influence on reinforcement loads. Results of simple statistical analyses to evaluate the ratio of predicted to measured peak reinforcement loads in geosynthetic walls were telling: the AASHTO Simplified Method results in an average ratio of measured to predicted loads of 0.45 with a coefficient of variation (COV) of 91 percent, whereas the proposed method results in an average of 0.99 and a COV of 36 percent. The proposed method remains accurate up until the point at which the soil begins to fail (approximately 3 to 5 percent strain). For steel reinforced MSE walls the improvement was more modest: AASHTO's Simplified Method results in an average ratio of predicted to measured loads of 1.12 with a (COV) of 45 percent, whereas the new K-Stiffness Method results in an average of 0.95 and a COV of 32 percent. The objective of the method is to design the wall reinforcement so that the soil within the wall backfill will not reach a state of failure consistent with the notion of working stress conditions. This soil failure limit state is not considered in the design methods currently available, yet, given the research results presented herein, is likely to be a controlling limit state for geosynthetic structures. The fruit of this research is a more accurate method for estimating reinforcement loads, thereby reducing reinforcement needs and improving the economy of reinforced soil walls. The scope of this research was limited to reinforced soil walls that utilize granular (non-cohesive, relatively low silt content) backfill.
Behaviour of Two-Tiered Geosynthetic-Reinforced Soil Walls
INAE Letters, 2019
The literature studies and current design methodologies of reinforced soil wall show increases in tensile stresses in reinforcement with increase in height of wall. This results in decrease of spacing between reinforcement and ultimately increases in cost of construction. Alternatively, the reinforced soil wall can be constructed in tiered fashion to improve aesthetic and reduce cost of construction. This paper focuses on the performance of two-tiered-reinforced soil-retaining walls with different offset lengths. A numerical model of geosynthetic-reinforced soil-retaining wall with a concrete-block facing reported in literature is simulated using commercial finite element software ANSYS. The backfill soil is modelled using the Drucker-Prager plasticity model. The concrete facing is simulated as elastic material and reinforcement with non-linear material properties. The results obtained from numerical model are validated with those from physical model studies reported in literature. Using validated model parameters, two-tiered-reinforced soil walls with different offset lengths are simulated. Four models of 0 offset, 1.2-m offset, 2.0-m offset and 3.0-m offset are developed to study the effects of tiered wall. The offset lengths are determined as intermediate offset distance and large setback distance as per FHWA (2010). The walls are studied for horizontal displacement of facing, strain developed in backfill soil and in reinforcement layers. The maximum horizontal displacements of reinforced soil wall decrease with increase in offset length of tiered wall. By considering the strain variation in soil, two deformation zones-shear deformation zone near the facing and compaction zone below the upper tier facing-are identified. The strains in compaction zone of lower tier increase with increase in offset length. The reinforcement strains in top reinforcement layer of lower tier decrease with increase in offset length. Keywords Multi-tiered-reinforced soil wall • Backfill strain • Numerical model • ANSYS